One of the study's authors, David Burnham, said the results showed that civil rights enforcement dropped across the board in President Bush's first term in office. "Collectively, some violators of the civil rights laws are not being dealt with by the government," Professor Burnham said. "This trend, we think, is significant."

It is unlikely the decline has occurred because of fewer civil rights violations occurring, the study suggests. The number of complaints about possible violations received by the Justice Department has remained at about 12,000 annually for each of the past five years.

The largest number of prosecutions brought by the Justice Department overwhelmingly have been for drug crimes.